Your ProMix will work fine. I don't know how helpful the mycorrhizea are for winter sowing, but won't hurt either :) It's a general all-purpose peat-based growing medium, just what you want for winter sowing. And not available here or I would try it myself one year, I get a generic type that one of our local nurseries mixes and bags for us.

None of the good potting soils contain 'soil', they are all soil-less mixes. Confusing, I know :)

THANK YOU !!! I always "second guess" myself and didn't make good notes last year (I will today!) I had 21 jugs done before I started to worry. I'm now on to do more! Thanks again for the fast reply.

That's what I've been using for the past several years! I order a big 3.8 cubic foot bale each year from the local Ace Hardware. They have it shipped to the local store from their warehouse. It seems to be a good potting mix for wsing.

You don't want to have much or any topsoil or compost in the potting mix, because over time these compact down in the container and this reduces oxygen available to plants' roots, also impedes drainage.